Using NK CR22® duplex stainless steel of 22%Cr-5.5%Ni-3%Mo, the extensive research has been carried out to analyze influences of various types of thermal cycles on corrosion resistance. Special attention was paid to the resistance to pitting corrosion in the weld heat affected zone (HAZ) through the complicated metallurgical aspect.

The optimum range of welding heat input exists for the improvement of pitting corrosion resistance in the HAZ. Lower heat input brings about the deterioration of the resistance near the fusion line, higher one on the contrary degrades the HAZ apart from the fusion line. Both these phenomena are closely related to the sensitization of grain boundaries caused by the precipitation of chromium nitrides.

Solution annealing is much effective in giving satisfactory pitting resistance in the HAZ. The annealing at high temperature over 1100°C, however, rather increases the susceptibility to pitting corrosion also by the sensitization of ferrite boundaries. Furthermore, the characteristics of the HAZ in the case of multi-pass welding are also mentioned, reflecting the girth welding of linepipe.

Subject
Corrosion rate, Microstructure, Precipitates, Welding, Solution annealing, Heat, Sensitization, Pitting, Corrosion resistance, Ferrite, Annealing, Grain boundary, Austenite
© 1986 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
1986
Association for Materials Protection and Performance (AMPP)
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